This invention relates to electrode structures for spark plugs, flame-front sensors, ionization sensors and the like, such as used in a generally automotive engineering context, and more particularly to a method and apparatus for fixing the central electrode of such devices within a surrounding insulating housing.
Conventional methods for sealing center electrodes within an insulating housing requires adequate spacing between the parts, centering procedures requiring additional tooling, and the infusion of special sealing powders within circumferentially extending gaps provided in the parts to be assembled. Moreover, the assembling and sealing steps for the various parts of the electrode structure, such as the center electrode, the insulator and the housing therefor must be timely separated to thus allow each step to be individually performed. As in most cases of spark plug manufacturing, a rolling and setting is also required in the course of the assembling process, as is well known in the art. Modern high efficiency combustion chambers in automobile engines now require that such electrode devices be used for sensing operating conditions and that such sensors or probes be accurately located, often in places where space is at a premium if not indeed severely limited. It is therefore necessary to reduce as much as possible the dimensioning of such electrode structures and probe devices in order to facilitate their installation, as well as their operation within confined areas.